A Quantitative Analysis Of Wing Pitching In Insect Flight

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Bergou, Attila

Abstract

The flying ability of insects is spellbinding: dragonflies can catch their prey in midair, mosquitoes have an intricate in-flight mating ritual, honey-bees are able to land precisely on a small flower. Even the minute fruit fly can accurately induce sudden flight maneuvers in milliseconds. To gain an understanding of how insects are able to perform these feats, scientists and engineers have, for more than a century and a half, pursued the principles behind how insects fly. This research has lead to many breakthroughs in our understanding of the behavior and force production of flapping wings. Despite such successes, many aspects of how insects are able to maneuver and precisely control their flight with such apparent ease, remain poorly understood. Insects control their flight by altering the motion of their rapidly beating wings. Therefore, in this thesis, we ask how insects actuate their wings. We focus mainly on a single degree of freedom of the wings: their orientation as they slice through the air, termed the wing pitch. This particular motion is chosen because of the sensitivity of the aerodynamic forces on both fixed wing and flapping flight to changes in wing pitch. The major results of this thesis are contained in Chapter 2-Chapter 5. In these chapters, we build a quantitative understanding of how insects pitch their wings. This part of the thesis culminates in Chapter 5 where we show how insects modulate wing pitching to induce flight maneuvers. We briefly summarize each chapter below. In Chapter 2, we analyze the hovering wing kinematics of insects and find that they do not do any positive work to pitch their wings. The wing inertia and aerodynamic forces both tend to rotate the wing, suggesting that wing pitching is largely passive. In Chapter 3, we describe the methods we developed to measure and visualize the kinematics of freely-flying fruit flies. In Chapter 4, we analyze the kinematics of freely-flying fruit flies and find that the pitching motion of insect wings can be understood by modeling the viscoelastic properties of the wing joints. In Chapter 5, we analyze the motion of maneuvering fruit flies and find that these insects turn by modulating their wing pitch, in effect rowing through the air. We show that their flight dynamics ultimately derive from fine-tuned biomechanical properties of the wing hinge with only subtle actuation by the musculature. The second part of the thesis focuses on the numerical methods used throughout this work. In Chapter 6, we describe the aerodynamic models used to compute the forces on insect wings. Finally, we end in Chapter 7 with a discussion of a topic somewhat separate from the rest of the thesis: we introduce a genetic programming method that determines symbolic relationships between variables from time-series measurements. We apply this method to finding an improved quasi-steady model for the aerodynamic torque that rotates a two-dimensional falling plate.